B737-800 flight crew reported a complete loss of pressurization at cruise altitude and that standby ...

Attributes
ACN	1586406
Time
Date	201810
Local Time Of Day	0601-1200
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	VMC
Aircraft 1
Make Model Name	B737-800
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Route In Use	Direct
Flight Plan	IFR
Component
Aircraft Component	Pressurization System
Person 1
Function	Pilot Flying Captain
Qualification	Flight Crew Instrument Flight Crew Multiengine Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Total 20000
Person 2
Function	Pilot Not Flying First Officer
Qualification	Flight Crew Multiengine Flight Crew Instrument Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Aircraft Equipment Problem Critical

Narrative:

At 37;000 feet the auto fail light illuminated on the air conditioning panel along with the master caution light. The pilot monitoring started the QRH procedure for the auto fail light. During the procedure the cabin was uncontrollable; the cabin altitude went above 10;000 feet and the masks dropped in the cabin. Both crew members donned oxygen masks and initiated an emergency descent. We established communications with the flight attendants and determined all in the cabin were on oxygen and no one had problems at this time. We [notified ATC]; diverted to ZZZ; safely landed the airplane and taxied to the gate.during the QRH procedure; we could not extinguish the auto fail light and the cabin became uncontrollable. Small inputs to outflow valve would not correct the situation.

Original NASA ASRS Text

Title: B737-800 flight crew reported a complete loss of pressurization at cruise altitude and that standby control did not recover the system.

Narrative: At 37;000 feet the Auto Fail light illuminated on the air conditioning panel along with the master caution light. The pilot monitoring started the QRH procedure for the Auto Fail Light. During the procedure the cabin was uncontrollable; the cabin altitude went above 10;000 feet and the masks dropped in the cabin. Both crew members donned oxygen masks and initiated an emergency descent. We established communications with the flight attendants and determined all in the cabin were on oxygen and no one had problems at this time. We [notified ATC]; diverted to ZZZ; safely landed the airplane and taxied to the gate.During the QRH procedure; we could not extinguish the Auto Fail light and the cabin became uncontrollable. Small inputs to outflow valve would not correct the situation.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.